The invention relates to a method and a radio station for transmitting data packets in a radio communication system, in particular in a mobile radio system.
In radio communication systems, information (such as voice, image information or other data) is transmitted with the aid of electromagnetic waves over a radio interface between a sending and a receiving radio station (base station and mobile station). The electromagnetic waves are radiated using carrier frequencies lying in the frequency band provided for the respective system. Frequencies in the frequency band of approximately 2000 MHz are provided for future mobile radio systems employing CDMA or TD/CDMA transmission methods over the radio interface, for example the UMTS (Universal Mobile Telecommunications System) or other 3rd-generation systems. Frequency Division Multiplex Access (FDMA), Time Division Multiplex Access (TDMA), or a method known as Code Division Multiplex Access (CDMA) here serve to distinguish the signal sources.
As part of the standardization of the UMTS standard, methods are currently being specified which support efficient transmission of data packets. So-called hybrid ARQ (HARQ) methods are an important technology in this area. Hybrid ARQ methods derive their advantage from the fact that incorrectly received data packets are stored in a storage facility (buffer) in the receiving device so that they can be combined with succeeding, repeated and, where applicable, modified transmissions of the data packets. In contrast to known pure ARQ methods in which faulty data packets are rejected, this advantageously also makes it possible to benefit from faulty data packets to increase the quality of reception. The data packets which are saved in this receiver-side buffer must be able to be read out very quickly so that no unnecessary delays occur in the data transmission and analysis. Storage facilities with this attribute are usually very expensive.
The system of what is termed High Speed Downlink Packet Access (HSDPA) which is currently specified for the UMTS also claims to be able to cater for different services with different Quality of Service (QoS) requirements simultaneously. These different QoS requirements of the data also necessitate a different form of processing of the respective data in the HARQ process. Furthermore it is necessary for the data packets of a service which arrive at the receiver to be reordered into the correct sequence. Typically, the receiver will not receive the data packets in the correct sequence since individual data packets can be disrupted during the transmission over the radio interface and have to be requested again via the ARQ mechanism, whereas other data packets originally transmitted at a later time are immediately received correctly.
In order to satisfy these requirements it is proposed to provide a separate HARQ process for each service. However, this disadvantageously leads to the size of the buffer required for the HARQ process having to be multiplied by the number of different services, which means that a large and expensive buffer or a plurality of buffers must be provided in readiness.